<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
  <style>
    *{
      margin: 0;
      padding: 0;
    }
    .box{
      width: 400px;
      height: 200px;
      background: #ccc;
      margin: 50px auto;
    }
    ul,li{
      list-style: none;
      float: left;
      margin: 0 2px;
    }
    ul{
      width: 100%;
      display: flex;
    }
    ul>li{
      flex: 1;
      height: 50px;
      background: skyblue;
      display: inline-block;
      position: relative;
    }
    span{
      width: 100px;
      display: inline-block;
      position: absolute;
      background-color: teal;
      top:50px;
      display: none;
    }
    li:hover>span{
      display: block;
    }
  </style>
</head>
<body>
  <div class="box">
    <ul>
      <li>
        <span>hello1</span>
      </li>
      <li>
        <span>hello2</span>
      </li>
      <li>
        <span>hello3</span>
      </li>
    </ul>
  </div>
</body>
</html>